In U.S. Pat. No. 3,941,552 there is disclosed a process in which a mixture of water/oil/coal is subjected to intense sonic agitation which shall be referred to in this specification as "sonification" sufficient to cause cavitation to thereby stabilize the mixture which can then be stored or piped and utilized as a fuel.
In co-pending application Ser. No. 194,117 filed Oct. 6, 1980, a continuation of application Ser. No. 915,854 filed June 15, 1978 and now abandoned, there is disclosed a method of beneficiating coal by mixing the same in particulate form with water and sonifying the mixture to reduce the size of the coal particles by, it is hypothesized the bombardment to which the particles are subjected because of the cavitation. During that process, the pyrites and ash are loosened from the coal particles and in the process of the application are separated out with the water.
In practicing the invention of U.S. Pat. No. 3,941,552, it sometimes occurred that the final product appeared grayish and exhibited an apparent instability in that the aqueous phase or, at least part of it appeared to be separating from the mixture.
While very careful proportioning of the water/oil/coal constituents of the mixture would eliminate this apparent instability, it was not always possible in a continuous on-the-line production of the fuel to take such care, particularly if it was desired to change the sequence of mixing the constituents.
What had been occurring however, in the apparently separated fuel product, was that the coal and oil being naturally lyophobic or repellent to water, the oil acted as a bridging agent to wet the coal, and when the mixture was subjected to agitation, the oil and coal tended to agglomerate and to reject the water. Inasmuch as the water/coal/oil mixture had been sonified, it was determined that when the water was separated out from the agglomerated mass, it contained a great deal of ash.
The separating out of the ash from the mixture is of course desirable and with the experience just discussed, it was decided to modify the process to beneficiate the coal particulate and to include coarse grinding followed by froth flotation or other separation method, followed by wet grinding to a small uniform size, followed by sonification followed by an agglomeration step to rid the mixture of ash and water before finalizing the product.
It also became clear that if properly modified, the process which would include sonification at various stages, to enhance the reduction of particle size and the beneficiation of coal and the agglomeration of the materials, might also be used in a much wider application of separating solids from liquid suspending media by sonification and agglomeration.
A process for separating solids by agglomeration is disclosed in U.S. Pat. No. 3,268,071 which issued Aug. 23, 1966. That process is one for the agglomeration and separation of mixtures of two different physically separate particulate solids comprising minerals and metals for instance, from an aqueous suspendant liquid, one of the solids being hydrophobic and the second one of the solids being hydrophilic to the suspendant liquid. A bridging liquid is added to the mixture in the suspendant liquid, which bridging liquid preferentially wets only the hydrophobic solids to form a film over the wetted hydrophobic solids. The resulting mixture is then subjected to mechanical agitation and turbulent conditions to floccuate the wetted hydrophobic solids and to compact the resulting flocculates into spherical agglomerates of greater density then that of the suspendant liquid. The agglomerates are then separated from the remaining suspension by screening.
In Canadian Pat. No. 1,020,880 which issued on Nov. 15, 1977, "micro agglomeration" is used as a method for displacing the liquid suspendant of a mixture of particulate material and liquid suspendant. That method includes the provision of a mixture containing particles having surfaces which in part are resistant to wetting by an agglomerating liquid and included adding to such a mixture, to displace a substantial amount of the liquid suspendant therefrom, the agglomerating liquid at a specified ratio to the solids in the mixture, then agitating the mixture containing the agglomerating liquid in a mixing device until the particulate material is micro agglomerated from the liquid suspendant.
In Canadian Pat. No. 1,039,059 which issued Aug. 26, 1978, a method of separating inorganic material from coal is disclosed comprising providing the coal containing the inorganic materials in particulate form, as a suspension with a liquid hydrocarbon oil, mixing an aqueous agglomerating liquid which is immiscible with the liquid hydrocarbon oil with the suspension, mixing a particulate material having a hydrophilic surface with the suspension, agitating the suspension with the aqueous agglomerating liquid and particulate material having a hydrophilic surface mixed therewith, to agglomerate inorganic particulate materials in the suspension with the aid of the particulate material having a hydrophilic surface, while leaving at least a major portion of the particulate coal dispersed in the liquid hydrocarbon oil, and then separating the inorganic material from at least a major portion of the liquid hydrocarbon oil and pulverized coal.
In these various prior art publications, just discussed, the usual suspendant liquid is water and the bridging or wetting liquid is an organic liquid preferably insoluble in water, and preferably having high interfacial surface tension between it and the suspendant liquid. Typical bridging agents are benzene, and aliphatic hydrocarbon solvent, such as "varsol", kerosene, petroleum lubricating oil, liquid chlorinated biphenyl, fuel oil and combinations of these. Of course the suspendant liquid may comprise an organic liquid in which case water would be the preferred bridging agent although glycol, formamide phenol, hydroxylated organic liquids and other liquids which are substantially insoluble in the suspending medium, are also suggested.
It is noted that in the prior art methods, the suspendant, the particulate matter to be agglomerated and the agglomerating liquid are mixed and that mixture is agitated until agglomeration occurs after which the suspendant liquid is separated out.